1. Field
The present application relates to compositions and methods for detecting metal ions, such as lead ions, in a sample.
2. Description of the Related Art
Over the past decades, many analytical techniques have been developed for quantitatively determining trace lead ions. Potentiometric ion selective electrodes (ISEs) are known to be a low-cost tool for sensitive and rapid determination of lead ions. However, the detection limit of conventional liquid-contact polyvinyl chloride (PVC)-based potentiometric sensor has been restricted to micromolar range due to the undesired leaching and uptake effects. In addition, the operating lifetime of most of the currently available ion selective sensors for lead ions is generally no more than six months.
Various approaches have been taken to improve the detection limit by, for example, optimizing ion buffer by 1) adding ethylene diamine tetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) in the inner filling solution (IFS) that keeps constant trace primary ions at 10−13˜10−11 M, 2) using ion-exchange resins Dowex C-350, 3) introducing interfering ions Et4NNO3, 4) simply reducing primary ions in IFS to 10−7 M, 5) applying an external current to sensing membrane, 6) rotating membrane electrode sensor, 7) covalently bonding ionophore to polymer backbones, and 8) doping PVC with ionic liquids. However, none of these approaches can achieve both low detection limit and long sensor lifetime at the same time. There is a need for long-lasting electrode sensors that allows reliable detections and measurements for lead ions in a sample at trace levels.